Recently, short-distance wireless communication technologies have come before the footlights. The wireless communicating based on these communication technologies can establish the cordless communication between devices and terminals, thereby simplifying the device connection work and, at the same time, enhancing convenience because it is substantially unnecessary to select installation spaces of the cordlessly connected devices. The short-distance wireless communication is expected a great deal also as the transmission media for home networks for example, in which it not realistic to lay network cables because of their locality.
The short-distance wireless communication may be used, for example, not only for the data transfer between a computer main frame and its peripheral devices, but also for the data exchange between mobile information devices, and data and audio transmission between a telephone main body, a mobile music player, and a headset, and between a main phone and its cordless headset.
Bluetooth, which is a representative example of short-distance wireless communication, is the standard for providing a wireless connection interface applicable to a variety of industries and operated and managed by the Bluetooth SIG (Special Interest Group).
Bluetooth uses a global radio frequency called ISM (Industry Science Medical) band of 2.4 GHz and provides a total data transfer rate of 1 Mbps, in which a synchronous transmission channel of 64 Kbps available for telephone voice transmission and an asynchronous transmission channel for data transmission are provided. For the synchronous transmission channel, SCO (Synchronous Connection Oriented Link) transmitting is used for the application to line linking. For the asynchronous transmission channel, ACL (Asynchronous Connection Less Link) transmitting is used for the application to the data transmission based on packet exchange. The connection range of interconnected devices based on Bluetooth is about 10 meters, which can be extended to 100 meters with the aid of an additional amplifier.
The technical specifications of Bluetooth are largely divided into the core and the profile. The core defines the base of the wireless connection provided by the Bluetooth, while the profile, in developing a variety of functions and applications on the basis of the Bluetooth core and assembling them into equipment, is a collection of the technical requirements specified for each function to guarantee the mutual connectivity between the devices.
There are two or more Bluetooth profiles and, by combining them, one application (also called a usage model (or usage) is provided. Actually, a combination of profiles providing an application is implemented in each Bluetooth product.
For example, a variety of Bluetooth profiles are supposed, such as the profiles for automobiles, networks, printers, audio devices, and video devices in addition to the profiles for mobile phones and personal computers, for example. For example, for a profile for remote commander control for audio visual (AV) equipment, “Bluetooth AV Remote Control Profile” (AVRCP) may be mentioned.
Originally, Bluetooth is a wireless communication technology for providing interconnection between mobile terminals; but, obviously, this technology is also designed for the application to stationary equipment. For example, the wireless connection based on Bluetooth may be applied to the connection between a main phone and its cordless handset, a mobile music player and its headset, or a stereo unit (or other media players) and its speakers (or other output devices such as display monitors).
Application of the wireless communication based on Bluetooth to the interconnection of devices solves the problems of the connector-unique shapes and characteristics obliged at cable connection. In addition, because Bluetooth is a worldwide standard using a global wireless frequency band called ISM (Industry Science Medical) band of 2.4 GHz, the globalization of communication environments may be promoted with ease.
Bluetooth provides not only one-to-one alternate connection, but also the construction of one-to-many simplified wireless networks. Hence, the order of communication is maintained by giving the control capabilities to one of the devices interconnected in a Bluetooth communication environment. The device given with the control capabilities is called a “maser device,” while the other devices are called “slave devices.” A network in which the master device and the slave devices are in a communication state is called a “piconet.”
Within a piconet, “piconet synchronization” is provided, in which each Bluetooth device in the communication state has the same frequency hopping pattern and a time slot with reference to the master device. The time slot is formed by each device with reference to the Bluetooth clock provided by the master device.
Within a piconet, one master device always exists and this master device carries out communication by controlling its slave devices. In addition, within a piconet, each packet is received only between the master devices and each slave device, so that the slave devices cannot directly communicate with each other.
The maximum number of slaves which can communicate with each other within one piconet is specified to be seven. The maximum of one master device and the seven slave devices can constitute Bluetooth communication environment in one piconet.
In the Bluetooth communication, there is a demand for executing device control between the slave devices. For example, if the Bluetooth communication is introduced in the field of audio visual (AV) equipment, a stereo unit or a media player may be defined as a master device, while a TV receiver and a headphone as output targets or a remote commander for remotely operating these output devices may be defined slave devices. Within the Bluetooth piconet like this, it would be meaningless for the user if the stereo unit, the master device, cannot control the targets such as a TV receiver and a headphone and, in addition, the remote controller, a slave device, cannot performing TV tuning and volume setting or headphone volume setting for example. However, as described above, these direct communication between the slave devices is not supported by Bluetooth.
For example, there is “AV Remote Control Profile” (AVRCP) for one of the Bluetooth-compatible AV device control profiles. However, because Bluetooth can originally execute communication by constituting one piconet by one master device and two or more slave devices, this AVRCP control profile is intended to realize one-to-one communication between the master device and one slave device.
In order for a remote commander, a slave device, to control another slave device via the master device, a method may be used in which a mechanisms for realizing this configuration is newly defined to implement it as a new control profile. However, if control is implemented in which a slave device controls another slave device via the master device by use of the new control profile, this method cannot be applied to the existing devices based on only AV Remote Control Profile control.